Roofs perform an important function of protecting buildings from weather, such as precipitation and solar radiation. In recent years, the function of roofing as a shield against solar radiation has increased in significance as an area that can be improved to lower energy consumption in maintaining comfortable temperatures in buildings. Many of the attributes of roofing are shared with materials used to construct the sides of a building, e.g., the ability to exclude precipitation and reflect or otherwise diminish unwanted solar radiation. In the following disclosure, roofing material is referred to in several exemplary embodiments of the present disclosure, however, the teachings of the present disclosure could be advantageously employed in forming materials for construction of areas of a building other than the roof, e.g., the sides or siding of the building. One common type of roofing that is popular today is Bituminous (asphalt) roofing, which is aesthetically pleasing, economical and effective, as well as relatively simple to install. Bituminous (asphalt) roofing membranes have been known and used for many years for forming waterproof roofs for buildings, both residential and commercial. Most modern bituminous roofing membranes are formed around a fabric sheet made from polyester, fiberglass or the like. The fabric sheet is coated with bitumen (asphalt), that has been modified with one or more modifiers such as Atactic PolyPropylene (APP), Amorphous Poly Alpha Olefin (APAO), Thermoplastic Polyolefin (TPO), Styrene-Butadiene-Styrene (SBS), Styrene-Ethylene-Butadiene-Styrene (SEBS), or synthetic rubber, to name a few. The modifiers change the properties of the asphalt to increase its utility as a roofing membrane, e.g., to make it more elastic, have greater flexibility at low temperatures and greater heat resistance at high temperatures to prevent softening/flow and deformation from mechanical forces, such as those associated with maintenance personnel walking on the roofing membrane. A roofing membrane may be formed of a laminate of a plurality of types of modified asphalt, e.g., a layer of a first type may be formed on the bottom surface that has an increased adhesive grip on the roofing underlayment and a different layer may be used on the upper surface that has enhanced weather resistance, etc. Adhesive layers may be applied to the membrane to allow the membrane to adhere to a substrate and/or to adhere to an adjacent sheet of roofing membrane. The adhesive may be applied to limited areas, e.g., the edge, where the roofing membrane is intended to overlap. There are a variety of ways for attaching roofing membranes to roofs, such as the application of an adhesive that can be softened by a torch, by “hot mopping” molten asphalt composition to the roof upon which the roofing membrane is applied and adhered, nailing (in the case of shingles) and self-adherent adhesives.
Bituminous roofing frequently employs an upper surface embedded with granules. These granules impart color, texture, foot/shoe slip-resistance and weather resistance to the roofing membrane. The granular texture imparted by the embedded granules has a significant aesthetic/architectural impact on the roofing product. More particularly, the granular texture is typified by having numerous identifiable independent granules, the majority of which extend in three dimensions to optically convey a rough surface to the observer. A granular surface has a multitude of peaks and valleys, shadows and color variations over the surface when illuminated from a given angle and viewed from a given perspective. These features allow the surface roughness to be perceptible to the observer.
The color of a roof has a significant impact on the absorbance/reflection of solar energy and therefore has a significant effect on the amount of energy required to heat/cool a building having that color roof. In hot climates, roofs with greater reflectivity can reduce energy costs related to air conditioning (cooling). In recognition of this effect, government entities have passed laws and regulations pertaining to the color/reflectivity of roofs and established incentives and criteria for selecting roofing materials that result in lowered energy demand. Ratings exist (Energy Star®) to characterize roofing light/heat reflectivity relative to that irradiating a given surface—as a fraction or percentage. For example, the United States Environmental Protection Agency's Energy Star Reflective Roof Program calls for low slope roofs (2:12 or less) to have an initial minimum solar reflectance of 0.65 and an aged three-year reflectance of 0.50. For steep-slope (greater than 2:12) roofs, minimum initial solar reflectance is 0.25, aged three-year reflectance greater than 0.15. As of 2009, ENERGY STAR allows products to qualify for ENERGY STAR certification using the CRRC Color Family Groups in accordance with the CRRC Product Rating Program Manual CRRC-1. Reflectance requirements vary depending upon the standard making body, some requiring greater initial reflectance of low slope roofs, e.g., 0.7O (ASHRAE) or 0.72 (Chicago).
Given a source of reflective granules, it is an objective of roofing manufacturers to achieve maximum coverage of the dark-colored bituminous membrane with the granules and to avoid spaces between the granules through which the dark membrane can be seen and which decreases reflectivity and increases solar radiation absorption. One suggested approach to make a highly reflective roofing and/or siding product employs a supplemental coating of granules of smaller size to fill in the gaps left by larger roofing granules. In theory, the smaller granules help to fill in the dark asphaltic voids between the large granules. A problem raised by this approach is that it is difficult to embed, press in or adhere the smaller granules without further embedding or over-pressing the larger granules that have already been applied to the sheet, i.e., without causing larger asphaltic voids than were present before the second application of granules. This methodology also raises the problem of achieving workable sheet temperature and tension, e.g., around a turnover drum, an S-wrap on a production line or through a press section. If the sheet becomes too cool, the granules will not embed well and will fall off the sheet during production or after exposure to the elements.
The reflectivity of a given granule surface may be increased by applying a reflective coating to the granule surface of a finished roofing membrane, e.g., by applying a paint to the granular surface. This may be conducted after the roof has been installed on a building, or may be applied to the roofing membrane during manufacture in the factory. If applied on-site, painting a roof is a difficult and laborious process due to roof height, slope and weather conditions and the quality of the finished product is dependent upon the skill and reliability of the workman. In either case, known applied coatings typically have a negative impact on the textured appearance of the roofing product. More particularly, to avoid staining or asphalt “strike through,” a primer paint may be applied followed by a top color layer. Multiple layers of paint represent added costs and inconvenience and tend to obscure granule texture, diminishing the aesthetic value of the resultant product.
In another approach, granular roofing with small granules is painted during the manufacturing process or in the field to improve reflectivity. This approach virtually eliminates the granule texture and the associated aesthetic attributes, e.g., compared to a membrane with larger roofing granules.
In another approach, granular roofing with large granules is painted. Subsequently, small granules are applied to prevent staining or transfer from the asphalt or modified bitumen membrane. This composite is then painted with a white elastomeric paint to fill the gaps between the granules, causing the granules to be obscured under the white elastomeric coating.
In yet another approach, a modified bitumen roll roofing membrane is coated with a layer of reflective laminate as the membrane is exiting from a formation line. The reflective laminate is heat activated; and then cured. Controlling the sheet temperature, the visco-elastic properties of the laminate, as well as the proper amount of laminate to achieve Energy Star ratings without losing the granule look can be challenging. Therefore, alternative methods, apparatus and formulations for producing reflective, aesthetically pleasing roofing and/or siding material, remain desirable.
In addition to color/reflectivity limitations of crushed stone and other known materials used for making granular surfaces of roofing membranes, the granules also have a limited resistance to erosion when subjected to rainwater, and in particular acidic rainwater, which is common in many areas due to air pollution. Acidic rainwater can etch/dissolve roofing granules, diminishing their reflectivity and loosening their embedment within the asphalt layer, such that they may be displaced from the asphalt layer, e.g., when subjected to mechanical forces, such as wind, leaves, snow, rain and the foot traffic of maintenance personnel. In the latter instance, the loosening of granules can result in diminished traction for maintenance personnel. Accordingly, alternative methods and materials for forming roofing membranes with high reflectivity, durability and weather resistance, remain desirable.